Pulling-means drives are sufficiently known in the existing art, and are used in many apparatuses, including microscopes. Pulling-means drives encompass at least a first shaft, a second shaft, and a pulling means looping around both shafts in order to transfer a torque between the shafts.
For example, a zoom microscope (macroscope or stereomicroscope) encompasses at least two lens groups that are arranged shiftably along their optical axis in order to modify the magnification of the microscope. A zoom system of this kind known from the existing art is depicted, for example, in FIG. 1. Zoom system 100 that is depicted encompasses a motor 140 for electrical displacement of lens groups 110, 120. In addition, a manual displacement of lens groups 110, 120 is likewise known. Lens groups 110, 120 are arranged on a spindle 130, the spacing of lens groups 110, 120 from one another being adjustable by way of a rotation of spindle 130. Spindle 130 in turn is connected via a pulling means (belt) 150 to drive shaft 141 of motor 140. More-detailed explanations of FIG. 1 may be found below in the description of the Figures. In such pulling-means drives, zero-backlash force transfer with no substantial force acting on the motor shaft is aimed for. The pulling-means tension must be adjusted in defined fashion for that purpose.
In the existing art, the pulling-means tension is usually adjusted in several steps. Firstly a first adjustment is performed, the quality of which depends critically on the experience of the user making the adjustment. The tension that has been set is then determined, for example via the resonant frequency of the pulling means. The user must then, in a following step, increase or decrease the tension depending on the measurement result, and then measure the tension again. The total time expenditure depends significantly on the user's experience and precision, and also cannot be arbitrarily decreased given the measurement steps necessary; this makes the method complex and costly.
FIG. 2 depicts a further known possibility for adjusting the pulling-means tension, in which a tension element (tension pulley 200) acts resiliently on pulling means 150. More-detailed explanations of FIG. 2 may be found below in the description of the Figures. A disadvantage of this existing art is that an additional element that generates costs and requires installation space must be provided, which element moreover exerts forces on the pulling means and thus increases wear.
In FIG. 1, a prior art zoom apparatus for a microscope is schematically depicted in a side view and labeled 100 in its entirety. Zoom apparatus 100 encompasses a first lens group 110 and a second lens group 120, which are arranged movably relative to one another along their optical axis. Provided for movement of the lens groups 110 and 120 with respect to one another is a spindle 130 that comprises helically extending cutouts 131 and 132. Lens group 110 is in interaction with cutout 131; lens group 120 is in interaction with cutout 132. A displacement of lens groups 110 and 120 relative to one another can thus be achieved by a rotation of spindle 130 about its rotation axis A.
In the depiction shown, spindle 130 is driven by an electric motor 140 by means of a pulling means embodied as belt 150. For that purpose, a drive axle 141 of motor 140 executes a rotation about its rotation axis B.
FIG. 2 depicts, from above, a prior art zoom apparatus 100 (for example, according to FIG. 1). Motor 140 is installable inside the microscope by means of arrangement means 142, 143. A spring-driven tension pulley 200 is provided in order to define a pulling-means tension on belt 150. A disadvantage of the arrangement depicted is that an additional component is used, the physical and geometric parameters of which must be adjusted in defined fashion in order to achieve the desired pulling-means tension. An increased space requirement also exists.
In another known method, the pulling-means tension is initially adjusted, for example, by means of a spring. The motor is then manually immobilized (which already influences the tension previously set) and bolted down. Experience shows that this causes tilting and thus a change, usually an increase, in the spacing of axes A, B, with the result that the pulling-means tension can be impermissibly increased. This results in loading of the bearings and thus in increased wear.
The known methods furthermore have the disadvantage that the tolerances of the spring, of the belt length, and/or of the suspension points negatively affect the accuracy of the pulling-means tension.